This invention relates to porous carbon materials making use of plant-derived materials as raw materials and their production process, and also to adsorbents, masks, adsorbing sheets and carriers.
Background Art
In recent years, portable electronic equipment such as camera-integrated VTRs (Video Tape Recorders), digital still cameras, cell phones, portable information terminals and notebook-size personal computers are widely prevalent, and their size reduction, weight reduction and life prolongation are strongly desired. Keeping in step with this desire, developments are under way for batteries, especially secondary batteries having light weight and permitting the provision of high energy density as power supplies for portable electronic equipment.
Among these, secondary batteries, which employ lithium as an electrode reactant in a charge-discharge reaction and use its occlusion and release (so-called lithium ion secondary batteries), are highly prospective because they provide large energy density compared with lead batteries and nickel-cadmium batteries. In these lithium ion secondary batteries, carbon materials are extensively used as anode active materials at anodes (see, for example, Japanese Patent Laid-Open No. Sho 62-090863). Employed as such carbon materials to keep production costs low and to provide improved battery characteristics are, for example, cokes such as pitch coke, needle coke and petroleum coke and baked products of organic high-molecular compounds as obtained by baking and carbonizing furan resins, natural high-molecular materials and the like at appropriate temperatures (see, for example, Japanese Patent Laid-Open No. Hei 4-308670). Further, a technology that bakes an organic high-molecular compound to produce a porous carbon material having three-dimensional regularity is disclosed, for example, in Japanese Patent Laid-Open No. 2005-262324, which also suggests that the porous carbon material is usable as an anode active material.
Further, carbon materials obtained by baking crystalline celluloses are also used as anode active materials as such crystalline celluloses vary less in crystalline degree in comparison with synthesized high-molecular compounds (see, for example, Japanese Patent Laid-Open No. Hei 2-054866). These carbon materials can obtain large charge capacity compared with cokes. In the carbon materials obtained by baking the crystalline celluloses, however, occluded lithium ions are not readily releasable. High charging efficiency is, therefore, hardly available, resulting in the observation of a tendency that as a whole battery, the energy density becomes smaller.
Unused parts of plants such as vegetables and cereals are mostly discarded. Effective utilization of these unused parts is, however, strongly demanded for the preservation and improvement of the global environment. As one example of the effective utilization of such unused parts, carbonization treatment can be mentioned. It is also investigated to use, as an anode active material for lithium ion secondary batteries, a carbon material produced by carbonizing such a plant-derived material (see, for example, Japanese Patent No. 3565994, Japanese Patent No. 3719790, and PCT Patent Publication No. WO 96/27911).
Further, for patients suffering from a liver disease or kidney disease, the elimination of toxic substances by hemodialysis is performed. However, hemodialysis requires a special system and an expert technician, and moreover, gives physical and/or mental discomfort or pain to patients. Under such a background, oral adsorbents made of activated carbon and having high safety and stability to the body, such as KREMEZIN, are attracting attention (see Japanese Patent Publication No. Sho 62-11611). In addition, anti-obesity agents, antidiabetic agents, anti-inflammatory bowel disease agents, purine adsorbents and the like, which make use of activated carbon, have also been proposed. Applications, research and developments of activated carbon in the medical field are extensively under way.
In addition, to make a drug to effectively act in the body, it is desired to allow an appropriate amount of the drug to act for an adequate time. For this purpose, it is preferred to use a carrier that can control the release rate of the drug. Adsorption of the drug on such a carrier makes it possible to continuously release the drug at a predetermined constant level. Such a drug-carrier complex can be used, for example, as a transdermal preparation having transdermal absorbability and topical action that deliver the drug through the skin, or as an oral preparation. The carrier is composed, for example, of carbon having nontoxicity and chemical resistance, an inorganic material such as alumina or silica, or an organic material such as cellulose or polyethylene oxide. In recent years, however, some examples making use of carbon materials as carriers have been reported (see, for example, Japanese Patent Laid-Open No. 2005-343885). There are also reports on the sustained release of fertilizer by the use of activated carbon (see, for example, Japanese Patent No. 3694305).